The present invention relates in general to jet pumps and, in particular, to jet pumps having ceramic nozzles.
Jet pumps are well known. Typically a power fluid under relatively high pressure passes through a nozzle and aspirates into its stream a fluid to be pumped, say, well fluid. The combined stream, often referred to as production fluid, enters the throat of a Venturi and passes into a diffuser of the Venturi where the streams slow down to recover static pressure head.
One purpose for a jet pump is to remove well fluid that has considerable solid content from a petroleum well. An example of the solids is sand.
Solids in a well fluid may be erosive. The Venturi of a jet pump has a comparatively small passage, the throat, that the power and well fluid streams pass through at high velocity. The erosive power of solids at these high velocities may be considerable. This has led to the throats of jet pump Venturis being eroded away. The solution to these problems has been to make Venturis out of ceramic materials because these materials resist erosion.
One way that a ceramic Venturi has been held in place has been by cementing it at its ends to support structure.
The Venturi of jet pumps can be subjected to considerable pressure differentials across their walls. For example, the static pressure of power fluid augmented by gravity at a downhole location can result in pressures of about 6,000 p.s.i. The pressure of well fluid of the formation may be about 1,000 p.s.i. Well fluid at 1,000 p.s.i. acting radially inward on a ceramic venturi opposes pressure within the Venturi and acting radially outward of about 6,000 p.s.i. with the net result that the Venturi is loaded in tensile hoop stress to a considerable degree.
Basic calculations indicate under the conditions just outlined that the ceramics used should be able to withstand this tensile hoop stress, but in fact failures have occurred. It is hypothesized that these failures in the ceramic are due to flaws in the material.
It is also known that ceramic materials are much stronger in compression than they are in tension.